Means using electron bunching apparatus for generating
ultra short-wave energy through use of cerenkov effect



June 28, 1966 PETRQFF 3,258,641

MEANS USING ELECTRON BUNCHING APPARATUS FOR GENERATING ULTRA SHORT-WAVE ENERGY THROUGH USE OF CERENKOV EFFECT Filed Feb. 5, 1963 2 Sheets-Sheet 1 a a l E INVENTOR. NHCHAEL D. PETROFF ATTORNEYS.

June 28, 1966 D, PETROFF 3,258,641

MEANS USING ELECTRON BUNCHING APPARATUS FOR GENERATING ULTRA SHORT-WAVE ENERGY THROUGH UsE OF GERENKOV EFFECT Filed Feb. 5, 1965 2 Sheets-Sheet 2 S w? F Y a a F T m E Rm ms m U m m NP T E T V A E m L m mNm E mum w m N i w I oow- Y B cans-1a (Aax) NERIBNE N United States Patent MEANS USHNG ELECTRON BUNCHHNG APPARA- TUS FUR GENERATENG ULTRA SHORT-WAVE ENERGY THRGUGH USE OF CERENKOV EF- FECT Michael D. Petroif, Los Angeles, Calif., assignor to National Engineering Science Co., Pasadena, Calif., a corporation of California Filed Feb. 5, 1963, Ser. No. 256,326 6 Claims. (Cl. 315-551) The present invention relates to improved means and techniques for generating electromagnetic energy having a wavelength of 1 centimeter to .1 centimeter, and is particularly applicable for the efficient generation of electromagnetic energy of shorter wavelength as, for example, submillimeter Waves; and also the present invention relates to improved means and techniques for bunching electrons, the same being particularly useful in a gen erator as described herein developing millimeter or submillimeter wave energy.

The present application discloses improvements in the type of generator described and claimed in my copending US. patent application, Serial No. 89,266, filed February 14, 1961, now Patent No. 3,178,656 and assigned to the same assignee and as to the subject matter common to this application and said application Serial No. 89,266, this application constitutes a continuation-in-part.

In general, the apparatus disclosed herein involves a high voltage beam of a bunched electrons passing through an apertured portion in a dielectric medium, the electrons in its passage through said apertured portion having a velocity greater than the phase velocity of electromagnetic waves in such medium for the production of so-called Cerenkov radiation. Such radiation is considered as being due to the effect of ditference between the velocity of the electrons in their passage through said apertured portion and that of its associated electric and magnetic fields in the dielectric medium. In general, the system described involves post acceleration of a bunched electron beam into an interacting structure with suppressed collection.

Electromagnetic or Cerenkov-type radiation is con sidered analogous to the shock wave accompanying a projectile travelling at supersonic speed. This type of radiation was reported by P. A. Cerenkov in 52 Physical Review, page 379, in 1937; and certain theoretical as pects of the same were discussed by 1. Frank and I. Tamrn in Read. Acad. Sci. URSS, 14,109 (1937). Low efliciency use of the Cerenkov effect for the production of millimeter wave energy is reported by Coleman and Enderby in the Journal of Applied Physics, vol. 31, No. 9, page, 1695, Sept-ember 1960.

The present invention involves new structural arrangements whereby Cerenkov-type radiation is produced more efiiciently and at much greater output power levels without the necessity of using a tightly bunched electron beam.

It is therefore an object of the present invention to provide an improved generator for millimeter waves that operates more efficiently and with the production of greater power outputs than was heretofore considered possible.

In achieving these results, the apertured dielectric medium is disposed in an electrostatic structure which ice provides a uniform electrostatic field within the same, such structure being charged at a sufficiently high electric potential, to accelerate the electron beam to a sufficiently high velocity immediately before entering the dielectric medium such that the Cerenkov effect is realized during the time that the electrons drift through the dielectric medium, and the potential energy of the electrons defines an electrostatic well. The arrangement is such that electrons, upon entering the well, are accelerated by the potential applied to the electrostatic structure enclosing the same, the electrons then drifting through the medium without any substantial change in the potential energy, and after the electrons leave the medium, the same are decelerated with the result that the electrons leave the well with relatively small energy.

Another object of the present invention is to provide a generator of this character in which the electron beam accelerating means comprises a high voltage source from which substantially no current is drawn in operation of the generator, thereby allowing use of a small high-volt age source.

Another object of the present'invention is to provide means and techniques for bunching electrons.

Another object of the present invention is to provide an arrangement for accomplishing electron bunching involving an interacting structure in a potential well.

Another object of the present invention is to provide a dielectric tube resonator in conjunction with an electron decelerating field to achieve electron bunching.

Another object of the present invention is to provide an arrangement of this character wherein an electron beam passes through a resonator tube which is maintained in a potential well for energy modulation purposes.

Another object of the present invention is to provide a self-sustaining oscillator for millimeter waves employing the Cerenkov effect.

Another object of the present invention is to provide an arrangement of this character wherein the electron beam collector, which collects the electrons after passage through the dielectric medium, is biased such that improved energy-conversion efliciency results when used either as an amplifier or as an oscillator.

Another object of the present invention is to provide an arrangement of this character that provides efficient use of low-interaction impedance structures in conjunction with high impedance beams.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood -by reference to the following description taken in connection with the accompanying drawings, in which:

FIGURE 1 is generally a transverse sectional view through a structure embodying features of the present invention arranged as a generator.

FIGURE 2, comprising FIGURES 2A and 2B, illustrates graphically various voltage and energy relationships in the system shown in FIGURE 1 as well as the character of the electron beam, fields and radiation produced therein, with regions in FIGURES 1 and 2 being correlated by the use of identical letters.

FIGURE 3 is an enlarged view of a portion of the apparatus shown in FIGURE 1.

The arrangement shown in FIGURE 1 includes a conventional 4-kilovolt electron gun structure which incorporates conventional means for producing electrons, for accelerating the electrons and for focusing them in a beam 11 at region A. The electrons comprising such beam 11, in the form of a DC. current are accelerated between regions A and B and enter the dielectric tube resonator 12 for purposes of producing an energy modulation of the entering beam. After leaving the resonator 12 the electrons are decelerated in the region CD and then pass through the annular relatively low voltage electrode 13. The electrons are again accelerated in the region E-F and then drift through the quartz Cerenkov coupler 14 wherein the desired radiation indicated by the lines 148 is produced, such radiation being reflected by the reflecting plate 15 in the direction indicated by arrows 16 whereby such radiation produced in coupler 14 is directed out through the output window 18.

This reflecting plate 15 is apertured at 15A to allow the electron beam to pass therethrough. The electron beam is decelcrated in the region G-H and impinges on the beam collector 19 after passing in succession through the apertured portion 20A in casing 20 and apertured portion 21A in the secondary repeller electrode 21.

It will be seen that a bunched electron beam is present at region F and enters the Cerenkov coupler 14, bunching of the electrons being accomplished as a result of their energy modulation in the dielectric resonator tube 12 and subsequent deceleration in the region C-D. This bunched electron beam, accomplished by deceleration of the energy modulated electron stream, is accelerated in the region E-F such that the then-accelerated bunched electron beam produces Cerenkov-type radiation when and as the beam drifts through the Cerenkov coupler 14.

The particular means whereby the bunched electron beam is produced forms an important part of the present invention and involves the resonator tube 12 to which modulating energy is transferred via waveguide 25 (FIG- URES l and 3), a portion of the wave guide 25 being illustrated in dotted lines in FIGURE 1 with one end of the waveguide 25 terminating, as illustrated in FIGURE 3, adjacent a portion of one end of the tube resonator 12 and with the other end of the waveguide 25 receiving its energy from input pickup horn 28 positioned to receive energy through the input window 30 from the modulating source 31.

v The speed of the electrons entering the resonator tube 12 is substantially equal to the speed, i.e., phase velocity, of the wave in the interacting structure of dielectric tube resonator 12 for achieving energy modulation of the electron beam 11. The wave developed in the resonator tube 12 is a TM wave as indicated in FIGURE 2A. As shown, the TM wave is symmetrical about its longitudinal axis.

While the resonator tube 12 is preferred, other interacting structures may be used for accomplishing energy modulation of the electron beam. Such other structures may, for example, be a dielectrically loaded waveguide, a disc-loaded waveguide or a multiple-wire helix. In some cases, a cylindrical cavity or series of coupled cavities through which the beam passes in succession may be used. In each case, the interacting structure, illustrated as a tube resonator 12, is disposed within a metal cage, similar to a Faraday cage 32 which in this case is maintained at a relatively high potential.

This case 32 as illustrated comprises two apertured and aligned generally annular metal sleeves 32A and 32B secured together by a series of bolts 32C and stationarily mounted within the metal tube 34 to which the positive terminal of a ZOO-kilovolt source 36 is connected for maintaining the tube resonator 12 within what is termed a potential well, as discussed in more detail in connection with FIGURE 2B. These two metal sleeves 32A, 32B each have their apertured portions 32C and 32D aligned with the apertured portion in the tube 12 by annular curved walls as illustrated, the curvature of the walls being shaped to establish a graduated electrostatic field that interacts with the electron beam at the apertured portions 32C and 32D.

This electrostatic cage 32, with the tube 12 mounted therein, is thus mounted as a unit on the tube 34 and the tub-e 34 has its left-hand end in FIGURE 1 adjustably mounted by means of a conventional bellows construction 40 on stationary tubular ceramic insulator 41 for alignment purposes. An intermediate portion of the tube 34 may also be resiliently mounted with respect to the insulator 41 by the bellows 42 which has a portion sandwiched between an end of the tubular insulator 41 and an end of a grounded metal tube or housing 43. This housing 43 has circular opening 43A through which the electrode support 13A sealingly extends, the particular sealing means used, as illustrated, comprising an alignment bellows 45 whereby the generally doughnut-shaped electrode 13 on the support 13A may be adjustably aligned with respect to the electron beam. This electrode 13 is connected to the positive terminal of a 4-kilovolt source 47 which, as indicated previously, produces a deceleration of the electron beam in the region C-D for purposes of effecting a velocity modulation or bunching of the previously energy-modulated electron stream.

Referring again to the tube resonator 12, it is seen that it is supported within the cage structure 32 in the following manner. The tube 12 is sandwiched between two aligned apertured rings 32E and 32F by bolts 32G and 321-1 with ring 32E being mounted by bolts 32C to ring 32] which may be secured as, for example, by welding to the tube 34. This tube 34 has an opening 43A through which the aforementioned electrode support 13A and electrode 13 extends; and a portion of the tube 34, as illustrated, is formed to provide a channel 34C through which waveguide 25 extends.

The second beam interacting structure, i.e., the quartz coupler 14, is in similar manner, mounted within the metal housing 59 to which the positive terminal of the ZOO-kilovolt source 36 is also applied through tube 34 which serves to mount the cage 50 and its surrounding metal cage that includes the two aligned apertured annular elements and 56 which, together with the cage 50, are secured to the tube 34 using annular web member 57 and fastening screws. The apertured portions 55A and 56A are defined by annular curved walls for producing a graduated electrostatic field on the electron beam passing thereth'r'ough. The electrode member 56 is also suitably apertured to allow a transmission of energy from the modulating source 31 to the input pickup horn 28 and also to allow passage of the developed millimeter energy through the output window 18.

The secondary repeller electrode 21 is insulatedly mounted on the grounded case 43 and has applied thereto a negative voltage from source 60 which has its positive terminal grounded. The beam collector electrode 19 is grounded. The electrode 21 and collector 19 all mounted on the casing 43 by the annular sealing structure 62 whereby vacuum conditions for the electron beam are maintained.

Preferably, as shown, the electron gun 10 is also supported by a bellows-type construction 65 on the stationary end wall 66 to allow some adjustment in alignment of the electron beam.

The electrons in the bunched beam at point or region E are insutficient to produce the Cerenkov effect. The electrode 55 serves to accelerate the bunched electron beam to a sufficiently high velocity to achieve the Cerenkov effect in the dielectric material 14 which preferably is of quartz and has the apertured portion or bore 14A extending therethrough through which the bunched electron beam passes or drifts. This bore 14A may have a diameter of approximately 1.0 millimeter and the dielectric medium may be approximately 5 centimeters long. The cage 50 is generally cup-shaped with a central aperturned portion 50A and a thin helical wire lines the apertured portion MA and is electrically interconnected with the cage 50. The pitch of the helix is such that any electromagnetic waves propagated on it travel with a velocity substantially lower than that of the electrons in the beam. As seen in the drawing, the dielectric medium 14 is defined generally by two conical portions with the conical portion of larger diameter being snugly fitted within the electrode 50. Also, as seen, the righthand end of the coupler M is conically recessed.

The DC. voltage source 36, connected to the electrodes 55, 56 and 50, is of sufficiently high value to establish the depth of a potential well so that the bunched electrons in region E are accelerated and enter the well at 55A travelling with velocities larger than the speed of waves in the medium 14, i.e., on entering the well the electrons have an energy equal to the well potential. After passing or drifting through the medium apertured portion 14A and radiating some of their energy via Cerenkov effect, the electrons leave the potential well at 56A and impinge on the collector electrode after being decelerated by the secondary repeller electrode 21.

It will be observed that the bunched electrons are accelerated and thus gain energy in their transit from the point or region E to the point or region F (or 55A); and that such electrons are decelerated and thus lose energy in their transit between regions G and H. Also, electrons emerging from the potential well at region G have their energy lowered from their value at point or region F substantially only by the amount of energy such electrons contribute to the Cerenkov radiation.

The geometry of the conducting electrode 55 is such that the bunched beam is focused properly when it enters the beam hole at 55A. Calculations indicate that when a ZOO-kilovolt, .15 ampere beam enters at point or region 55A in parallel flow, it can traverse the entire length of the beam hole 14A in the dielectric without spreading enough to impinge on the walls of the hole. Should random electrons impinge on the Wall of hole 14A, the helical wire provides a leakage path for any such electrons lost from the beam.

The electrons in the beam enter the collector 19 with energies approximately equal to 4 kilovolt minus whatever energy each electron gives up in Cerenkov radiation inside the dielectric medium. Since no charge is deposited on the ZOO-kilovolt electrode 50 in the process, the power needed to maintain this voltage is negligible. The beam power inside the hole 14A in the dielectric is equal to approximately 30 kilowatts. To maintain this high power where only a small fraction of it is used, practically no power is consumed in the charging power supply. Thus the supply source 36 is a relatively small and simple component of the system.

The electrons in the bunch beam passing through the hole 14A and the coupler 14 have a velocity equal to approximately .70 where c is the velocity of light in free space. The index of refraction of the dielectric material is substantially equal to 1.94. Consequently, the condi tions for Cerenkov radiation are satisfied and the waves are radiated with a propagation vector making an angle of 42 with respect to the longitudinal axis of the dielectric medium as indicated in FIGURE 2. These waves are incident on the conical surface 14a and are internal reflected to be further reflected internally. These waves incident on the conical surface boundary MD of the medium at the Brewsterian angle and are totally refracted in such a way that outside the medium the propagation vector is parallel to the axis. The resultant parallel beam of transverse magnetic waves, illustrated by the lines 14B in FIG- URE 1, are reflected by the mirror through the output window 18. These waves can be used either directly as a beam or collected into a waveguide using a coaxial horn pickup. The power radiated by the beam may be calculated. The wave power generated is approximately 10 watts for current of approximately .15 ampere.

A beam current of .15 ampere that loses 10 watts of power requires that the average energy loss of individual electrons in the beam be about 67 volts. Consequently, in passing through the dielectric, the electron velocity between regions F and G drops only approximately 025%. The electron beam is therefore essentially a constant velocity beam which drifts through the hole 14A.

The diameter of the hole 14A is of importance in establishing the intensity of radiation of different frequencies. The hole diameter is such that radiation at a frequency of 300,000 megacycles predominates with radiation of higher frequencies, i.e., at the harmonic frequency of 300,000 megacycles, being considerably lessened.

It will be thus seen that the arrangement shown in FIGURE 1 operates essentially as a power amplifier for amplification of the 300,000 inegacycle power supplied from source 31 with the increase power being obtained from the energy supplied to the electron beam in the electron gun 10.

The arrangement may be modified to operate as oscillator and in such case some of the energy from output window 18 is transferred by suitable means to the input window 30 for producing a regenerative effect and thus oscillations. For this purpose the feedback energy may be applied through a directional coupler interposed between the output window 18 and input window 30. Additionally, if desired or necessary, suitable attenuator and1 phase shifting means may be used in the feedback pat Increased eflic-iency results when the electron collector 19 is at a potential more comparable to the electron accelerating potential supplied to the electron gun. This is accomplished by applying a biasing potential to the secondary repeller electrode 21 as shown in FIGURE 1.

The electron gun It) in FIGURE 1 has a negative 4,000- volt potential applied to its cathode from the negative ungrounded terminal of source 7 0 as the electron accelerating potential, the anode of the gun being grounded. The electron collector 19, in the absence of the secondary repeller electrode 21 and source 60 connected thereto, may be maintained at a potential at approximately 2700 volts with respect to ground in those cases where the secondary repeller electrode 21 is not used. By these expedients the collector '19 has a potential to produce a greater deceleration of electrons and consequently the electrons impinge on the collector 19 with lower velocities, thereby dissipating less heat.

Of course, it is preferred that the voltage conditions near the collector electrode be such that there is an assurance of collection of all electrons in the beam with a development of the minimum amount of heat.

One of the important features of the present invention is a provision of two electron beam interacting structures, i.e., the interacting structure involving dielectric tube resonator 12 and the other involving the Cerenkov coupler 14. With respect to the tube resonator 12, the same may be in the order of 21 wavelengths long. Since the electrons are very energetic, velocity modulating is exceed ingly small and the beam is energy modulated by an amount depending on its phase with respect to the wave in the structure 12. In the process of deceleration between regions C and D wherein the energy modulation manifests itself as velocity modulation and bunching takes place, the beam will be 'defocused. This defoeusing is of importance for the feasibility of bunching at submillimeter wavelengths. Defocus-ing prevents undue increase of the local plasma frequency in the beam which, as it turns out, greatly facilitates maintaining proper bunching.

Referring to FIGURE 2 which is intended to convey a physical picture of processes entering into the operation of the generator, there is illustrated for simplicity interacting structures only a few wavelengths long. No attempt is made to represent space charge effects. The modulating RF voltage in the bunching structure 12 is approximately 800 volts in amplitude. Also, as illustrated in the FIGURE 2, essentially no bunching or debunching takes place within the two potential wells, i.e., within the electrostatic structures or Faraday cages 32 and 55. The dotted line 80 in FIGURE 2 represents energy and posi tion of a sequence of electrons passing point B at equal intervals of time. The graph 81 represents potential energy at corresponding points. Differences in ordinates in graphs 80 and 81 represent kinetic energy. This representation of the electron beam is very useful for showing important phases of the bunching and coupling processes. In the first interacting structure 12, the electrons gain or lose energy as they travel together with the wave. Since the wave and electron velocities are matched, they will steadily gain or lose energy in proportion to distance of travel and the axial field strength of the wave corresponding to their positions. The dots, as shown in FIGURE 2, indicative of the beam current will generate a sinusoidal curve with amplitude increasing linearly with distance between points B and C. Between points D and E the electrons leave the potential well and are decelerated. The wavelength of the sinusoidal curve decreases accordingly. Between points D and E the energy modulation that the electrons received when in the interacting structure manifests itself as a pronounced velocity modulation. Consequently, the higher energy electrons will be moving appreciably faster to the right than the lower energy ones. As a result, the sinusoidal curve becomes more and more tilted, i.e., bunching develops. This tilted wave curve serves the same purpose as an Applegate diagram to illustrate bunching. By counting the number of dots per unit distance along the axis, we have an accurate picture of the charge density of the beam. The density of shading in the beam 81 in FIGURE 2A is proportional to charge density. Between points E and F the electrons are reaccelerated and hence wavelength of the now strongly tilted sinusoid is again increased. On entering the interacting structure 14, the bunched beam generates an EM wave in the structure acting to oppose most strongly the motion of the charge in the most dense regions of the beam. The field lines shown in the structure give the phase of the wave with respect to the bunches. Most of the electrons therefore lose energy to support the field. The relatively smaller part of the beam charges between dense regions gains energy. This results in a very peculiar additional distortion of a sinusoidal curve between points G and H wherein the electrons are again decelerated. The density of dots between H as a function of energy gives a fair picture of the energy spectrum of the spent beam. As long as the potential of the collector 19 is such that the lowest energy electrons of this spectrum are not completely decelerated and therefore not reflected back to the high potential region, all of the electrons of the beam can be collected with a properly designed beam trap or suppressed collector.

In the use of long interacting structures, the plasma wavelength of the beam must be larger than the length and spacing of the interacting structures, otherwise both bunching and coupling at the output are impaired. Using beams of voltages in excess of 100 kilovolts overcomes this in part by virtue of higher electron velocities and therefore low densities.

If desired, the Cerenkov coupler 14 may be composed of two or more dielectrics or they can be made of artificial dielectric such as periodic arrays of conductors of small size. The principal advantage of such coupler is its simplicity, bandwidth and direct emission of the generated wave power which makes them ideal for quasi optical techniques for submillimeter waves.

A coaxial horn pickup can be used to collect the output power. Since the radiation mode emitted by the coupler is identical to that of the coaxial horn antenna, the col lection efi'iciency will be high. For special applications the output beam can be used directly.

While the particular embodiments of the present inven- 8 tion have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. A generator of electromagnetic waves comprising, means for producing a beam of electrons, means velocity-modulating said beam to produce a bunched beam of electrons, a dielectric material having an apertured portion therethrough through which said bunched beam passes, means accelerating said bunched beam to a linear velocity such that said linear velocity of said bunched beam passing through said apertured portion is greater than the phase velocity of electromagnetic waves in said material, said accelerating means comprising an electrode effectively encompassing said material, a high voltage source connected to said electrode, said velocity-modulating means comprising a dielectric tube resonator interacting with said beam, means supplying energy to said resonator to energy-modulate said beam of electrons, and a decelerating electrode interposed between said tube resonator and said dielectric material.

2. A generator of electromagnetic waves comprising, means for producing a beam of electrons, means velocitymodulating said beam to produce a bunched beam of electrons, a dielectric material having an apertured portion therethrough through which said bunched beam passes, means accelerating said bunched beam to a linear velocity such that said linear velocity of said bunched beam passing through said apertured portion is greater than the phase velocity of electromagnetic waves in said material, said accelerating means comprising an electrode effectively encompassing said material, a high voltage source connected to said electrode, said velocity-modulating means comprising a dielectric tube resonator interacting with said beam, means supplying energy to said resonator to energy-modulate said beam of electrons, and a decelerating electrode interposed between said tube resonator and said dielectric material, said dielectric tube resonator being disposed within a metal structure that is energized to define a potential well.

3. In an arrangement of the character described, a support, an electron gun mounted on said support, a pair of shielding structures insulatedly supported on said support, a first interacting structure in one of said shielding structures, a second interacting structure within the other of said shielding structures, electrode means between said shielding structures and insulatedly mounted on said support, means supplying energy to the first-mentioned interacting structure to produce an energy modulation of the beam, means applying to a relatively high voltage to each of said shielding structures, said second interacting structure interacting with the beam to produce radiation in accordance with energy of the beam, means applying a relatively low voltage to said electrode means between said shielding structures whereby an electron beam leaving the first interacting structure is first decelerated and then accelerated as it enters the second interacting structure, said second interacting structure comprising a dielectric shaped to produce radiation therefrom in a predetermined direction, a radiation mirror receiving radiation from the dielectric and having an apertured portion through which said electron beam may pass, said support carrying an optical window through which said radiation may pass from said mirror, and beam-collecting means for collecting electrons leaving said second interacting structure.

4. An arrangement as set forth in claim 3 including means carried by the support for aligning said shield structures with respect to the electron beam.

5. An arrangement as set forth in claim 3 including a repeller electrode mounted on said support between said second interacting structure and said beam collector.

6. An arrangement as set forth in claim 5 including aligning means carried on said support for aligning said electron-beam-producing means with respect to said shielding structures.

References Cited by the Examiner 5 UNITED STATES PATENTS FOREIGN PATENTS 9/ 1957 Great Britain.

OTHER REFERENCES Generation of Microwaves by Cerenkov Radiation, by Lashinsky, Proceedings of the Symposium on Millimeter Waves, 1959, pages 181-189.

Mueller 3153 Haeif 315-3 HERMAN KARL SAALBACH, Primary Examiner. Peter 313 239 X 10 GEORGE N. WESTBY, Examiner.

Brewer 3153.6

Petroff 315. .3 X S. CHATMON, JR., Assistant Examiner. 

1. A GENERATOR OF ELECTROMAGNETIC WAVES COMPRISING, MEANS FOR PRODUCING A BEAM OF ELECTRONS, MEANS VELOCITY-MODULATING SAID BEAM TO PRODUCE A BUNCHED BEAM OF ELECTRONS, A DIELETRIC MATERIAL HAVING AN APERTURED PORTION THERETHROUGH THROUGH WHICH SAID BUNCHED BEAM PASSES, MEANS ACCELERATING SAID BUNCHED BEAM TO A LINEAR VELOCITY SUCH THAT SAID LINERA VELOCITY OF SAID BUNCHED BEAM PASSING THROUGH SAID APERTURED PORTION IS GREATER THAN THE PHASE VELOCITY OF ELECTROMAGNETIC WAVES IN SAID MATERIAL, SAID ACCELERATING MEANS COMPRISING AN ELECTRODE EFFECTIVELY ENCOMPASSING SAID MATERIAL, A HIGH VOLTAGE SOURCE CONNECTED TO SAID ELECTRODE, SAID VELOCITY-MODULATING MEANS COMPRISING A DIELECTRIC TUBE RESONATOR INTERACTING WITH SAID BEAM, MEANS SUPPLYING ENERGY TO SAID RESONNATOR TO ENERGY-MODULATE SAID BEAM OF ELECTRONS, AND A DECELERATING ELECTRODE INTERPOSED BETWEEN SAID TUBE RESONNATOR AND SAID DIELECTRIC MATERIAL. 